JPH08302596A - Water absorbing sheet - Google Patents

Abstract

PURPOSE: To prepare a water absorbing sheet having liquid diffusion and temporary storage properties, water absorbing performance, and markedly improved in absorption rate especially when it is made into an absorbing material of a multi-layer structure. CONSTITUTION: A water absorbing sheet comprising a synthetic fiber and a cellulosic fiber. The cellulosic fiber in a fixed region of the sheet contains cross-linked carboxyalkyl groups of 0.35-0.8 substitution degree, the cellulosic fiber in a region except the above region of the sheet contains neither the carboxyalkyl group nor a cross-linking bond. Both of a highly water-absorbing region and a low water-absorbing region exist in the sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water absorbent sheet composed of synthetic fibers and cellulosic fibers. More specifically, the present invention is a mixture of synthetic fibers, cellulosic fibers having a carboxyalkyl group and a cross-linking bond, and cellulosic fibers having no carboxyalkyl group and a cross-linking bond, to diffuse and temporarily store liquid ( (Hereinafter referred to as “transfer performance”) and water absorption performance, and particularly regarding a water-absorbent sheet having a significantly improved absorption rate when used as an absorbent body having a multilayer structure, in the field of sanitary materials such as disposable paper diapers and sanitary products, and soil water retention. It can be widely used as a field of agricultural materials such as lumber and seedling raising sheet, a field of food such as food freshness retaining material and dehydration material, and a building material such as a sheet for preventing dew condensation of buildings.

[0002]

2. Description of the Related Art In recent years, a group of materials called superabsorbent resins have been known as absorbent materials for aqueous solutions containing salts such as water or saline. 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-absorbent material include, for example, starch obtained by graft-polymerizing acrylonitrile and then hydrolyzing it, starch obtained by graft-polymerizing an acrylic acid metal salt, and acrylic acid polymerized with a copolymerizable cross-linking agent. A large number of crosslinking resins, hydrolysates of methyl methacrylate-vinyl acetate copolymers, etc. have been proposed, and some of them have been put to practical use.

Cotton, pulp, paper, cloth, sponge, etc., which are known as traditional water-absorbing materials, absorb water by a capillary phenomenon, whereas the superabsorbent resin described above has a principle of absorbing water. Because it is osmotic, it can absorb much more water than capillarity. Such a highly water-absorbent resin has an excellent feature that it does not easily release water again even if pressure is applied in a water-absorbing state. For this reason, the applications of super absorbent polymers include disposable paper diapers, sanitary materials such as sanitary products, soil water retention materials, agricultural materials such as nursery sheets, food freshness preservation materials, food materials such as dehydration materials, and dew condensation on buildings. Widely used as building materials such as prevention sheets.

On the other hand, the present inventors 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,
By heating the cellulosic fibers to cross-linked carboxymethyl cellulose, a water-absorbent nonwoven fabric that maintains a sheet shape even after absorbing water and has excellent wet strength has been proposed (Japanese Patent Application No. 5-217912). However, if the water-absorbent sheet-like material as described above is used only as a single sheet and the water-absorbing ability is insufficient, it is unavoidable to use it as an absorbent body having a multilayer structure of two or more sheets. Then, so-called gel blocking occurs in which the entire sheet swells and loses water permeability. As a result, when the water-absorbent sheet on the liquid side to be absorbed absorbs water and causes gel blocking, the liquid diffuses into the second and subsequent water-absorbent sheets or the water-absorbent material used together with the water-absorbent sheet. Therefore, it takes a very long time to absorb the liquid, and when the amount of the liquid to be absorbed is large, the liquid leaks to the outside of the absorber.

[0005]

SUMMARY OF THE INVENTION In view of the above situation, the present inventors have found that even if a plurality of water absorbent sheets are stacked and used as an absorbent body having a multilayer structure, the permeability or diffusibility of a liquid due to gel blocking is not hindered. The water-absorbent material in the form of a sheet was earnestly studied. As a result, the known water-absorbent sheet, carboxyalkylating agent, alkali metal hydroxide,
Since the sheet containing cellulose is immersed in an aqueous reaction solution containing a cross-linking agent and water to carry out the reaction, there are cross-linked carboxyalkyl groups all over the surface and thereby the water absorption performance is remarkably improved. However, using such a sheet as a multilayer absorbent body,
It has been found that when a large amount of liquid is absorbed, gel blocking occurs as described above, the liquid permeability is impaired, and the liquid absorption rate is significantly deteriorated.

Therefore, the present inventors have made the above water-absorbent sheet that causes gel blocking uniformly contained in the entire cellulose fiber by impregnating the water-soluble reaction solution, and then carry out a reaction to impart water-absorbing performance to the cellulose fiber. The reaction is carried out by partially containing the reaction solution, the cellulose fiber of the water-absorbent sheet has a highly water-absorbing region having a crosslinked carboxyalkyl group, and such a group is also included. A water-absorbent sheet obtained by mixing and providing a low water-absorbing region having no cross-linking, even when using a plurality of absorbent layers having a multi-layer structure, the passage or diffusion of the absorbed liquid is not hindered, therefore water absorption They have found that a water-absorbent sheet having a remarkably excellent speed can be obtained, and completed the present invention. The object of the present invention is not to impair transfer performance (having both liquid diffusion and temporary storage properties) and water absorption performance even when absorbing a liquid, and it is remarkably excellent especially when it is used as an absorbent body having a multilayer structure. Another object of the present invention is to provide a water absorbent sheet having a different water absorption rate.

[0007]

The present invention provides a water-absorbent sheet containing a synthetic fiber and a cellulosic fiber, wherein the cellulosic fiber in a desired region of the sheet has a substitution degree of 0.35 to 0.35.
It has a crosslinked carboxyalkyl group of 0.8, and the cellulosic fibers of the portion other than the above-mentioned region of the sheet do not have a crosslinkage bond with the carboxyalkyl group, so that the sheet has a high water absorption region and low water absorption. The water-absorbent sheet is characterized in that areas are provided in a mixed manner.

As the synthetic fiber used in the present invention, a fiber made of a known thermoplastic resin can be used. Examples thereof include polyolefin fibers, polyester fibers, polyamide fibers, polyacrylic acid ester fibers, polyurethane fibers, and the like, and these are appropriately selected and used alone or as a mixture. Such a synthetic fiber is used in the form of a spunbonded non-woven fabric in which continuous filaments are formed into a sheet, a sheet or a non-woven fabric obtained by a card method or a wet method in which staples are laminated in a sheet form, a melt blown non-woven fabric, or the like. or,
The synthetic fiber may be a woven fabric, and the production method thereof is not particularly limited.

The fineness of the fiber is not particularly limited, and it can be used from extremely thin ones such as a melt blown nonwoven fabric to relatively thick ones such as a spunbonded nonwoven fabric, but the range is 0.02 to 10 denier. Preferably. When the fineness of the fiber exceeds 10 denier and becomes thicker, the flexibility of the non-woven fabric decreases, and the flexibility, texture and processability of the water absorbent non-woven fabric deteriorate. If the fiber fineness is less than 0.02 denier, it may be extremely difficult to produce fibers having stable properties. Examples of the cellulosic fibers used in the present invention include pulp fibers produced from wood, non-wood pulp fibers produced from plants, regenerated cellulose fibers and the like.

Pulp fibers produced from wood include
Kraft method of coniferous or hardwood wood, sulfite method, soda method, chemical pulp fiber produced by digesting by polysulfide method, refiner, mechanical pulp fiber ground into pulp by mechanical force of a grinder,
Waste paper pulp fibers may be mentioned, and these pulp fibers may be unbleached or bleached, if necessary, alone,
Alternatively, they can be used as a mixture. Non-wood pulp fibers include, for example, fibers obtained by pulping cotton, Manila hemp, flax, straw, bamboo, bagasse, kenaf, mulberry, sanpei, etc. in the same manner as wood pulp. As regenerated cellulose fibers, viscose rayon, which is prepared by spinning cellulose in a viscose form and then regenerated and spun in acid, is dissolved in copper ammonia solution and then regenerated and spun in acid. Copper ammonia rayon, N
Examples thereof include regenerated cellulose fibers obtained by spinning after dissolving in a non-aqueous cellulose solvent such as methylmorpholine-N-oxide.

In the present invention, a known method can be used as a method for producing a sheet containing synthetic fibers and cellulose fibers. For example, "Reseach Disclosure, 17060, Ju
ne 1978 ", JP-A-5-253160, JP-A-5-
277053, JP-A-5-285083,
JP-A-5-286100 and JP-A-6-17365.
As disclosed in, for example, a thermoplastic resin is melted by heating and spunbonded spunbonded nonwoven fabric composed of continuous long fiber filaments obtained by spinning, and a paper sheet obtained by making pulp fibers is laminated to form a paper. Inject high-pressure water jet from the sheet surface to entangle the long fibers and pulp fibers,
The composite sheet obtained by the integration method is excellent in flexibility, texture, workability, etc., and can be suitably used in the present invention.

Alternatively, a method may be used in which short fibers as synthetic fibers and cellulosic fibers are mixed in advance and a web is formed by a dry or wet method to form a sheet. In this case, it is necessary to partially bond the synthetic fibers to each other in order to keep the wet tensile strength of the sheet high. As a method of partially adhering synthetic fibers to each other, a known method can be applied as it is, a method of spraying an adhesive, a method of adhering by heating, a method of mixing heat fusion fibers and adhering by heating, a needle A method using a punch, a method using a stitch bond, or the like can be used.

In the present invention, it is preferable that the blending ratio of the synthetic fibers and the cellulosic fibers constituting the sheet is 1 to 19 cellulosic fibers to 1 synthetic fiber. When the ratio of the cellulosic fibers to the synthetic fibers is less than 1, the amount of the cellulosic fibers to the synthetic fibers is relatively small, and the water absorption amount of the obtained sheet is small. On the contrary, when the ratio of the cellulosic fibers exceeds 19, the swollen cellulosic fibers are likely to fall off when the obtained sheet is made to absorb water, and the wet tensile strength may be further reduced.

The cellulosic fibers in the desired region of the sheet of the present invention have high water absorption. In order to impart this high water absorption, first, the cellulose-based fiber in a desired region of the sheet is allowed to contain an aqueous reaction liquid composed of a carboxyalkylating agent, an alkali metal hydroxide, a crosslinking agent and water, and crosslinked by heating. Coupling and carboxyalkylation must be carried out, but such an aqueous reaction solution is disclosed in Japanese Patent Application No. 6-1873.
The water-soluble reaction solution used in No. 03 can be used as it is. As the carboxyalkylating agent used in this aqueous reaction solution, an alkali metal salt of halocarboxylic acid is used. As the halocarboxylate 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- Examples thereof include those having a carbon number of 3 or less such as bromopropionic acid alkali metal salts and the like, and these may be used alone or appropriately selected and mixed. In terms of cost, sodium monochloroacetate is cheap, so it is recommended to use it.

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. As the cross-linking agent, it is preferable to use a cross-linking agent that cross-links with cellulose in an alkaline aqueous reaction solution, has a boiling point as high as possible, and is close to non-volatile. In the present invention,
The step of adding the aqueous reaction solution to the cellulose fibers in the desired region of the composite sheet and then evaporating and removing the water is optionally included, in which case a crosslinking agent having a low boiling point that volatilizes during this step is used. Not preferable.

The cross-linking agent which can be used in the present invention includes ethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, polyethylene glycol diglycidyl ether, polyepoxy compounds such as diepoxybutane, divinyl sulfone and methylene. Divinyl compounds such as bisacrylamide, dichloropropanol, dibromopropanol,
At least one kind of polyvalent halogen compound such as dichloroacetic acid and polyvalent aziridine compound are appropriately selected and used. Epichlorohydrin, which is often used for cross-linking cellulose derivatives and can impart excellent pure water absorption performance, has a low boiling point, and thus needs attention when used.

The aqueous reaction solution is obtained by dissolving a carboxyalkylating agent, an alkali metal hydroxide and a crosslinking agent in water. The ratio of water to the total weight in this aqueous reaction solution is
Since the solubility varies depending on the type of carboxyalkylating agent or alkali metal hydroxide used, it cannot be specified unambiguously, but the smaller the proportion of water within the range of solubility, the aqueous reaction liquid is contained in the cellulose fiber, This is advantageous because it requires less energy cost in the subsequent evaporation of water. However, if the concentration is too high, the aqueous reaction solution becomes unstable and handling becomes difficult. Therefore, in the present invention, the ratio of water to the total weight of the aqueous reaction solution is 60 to 90% by weight when sodium hydroxide is used. The carboxyalkylating agent, alkali metal hydroxide and crosslinking agent are dissolved in water so that Since the solubility of this water varies depending on the kind of the carboxyalkylating agent, the alkali metal hydroxide and the crosslinking agent used, the lower limit value varies slightly. The mixing molar ratio of the carboxyalkylating agent and the alkali metal hydroxide is adjusted to 0.8 to 1.2 for the alkali metal hydroxide / carboxyalkylating agent. The more it deviates from 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% by weight based on the weight of cellulose.

Next, the aqueous reaction solution prepared as described above is added to the cellulosic fibers in a desired region of the sheet containing the synthetic fibers and the cellulosic fibers prepared in advance to obtain an aqueous reaction solution. The carboxyalkylation and the cross-linking agent react with each other only in the cellulosic fibers of the contained portion to impart high water absorption. When the aqueous reaction liquid is contained in the cellulose fiber of the sheet, the spread of the liquid-containing region due to the diffusion of the aqueous reaction liquid is suppressed, and in the aqueous reaction liquid in order to maintain a desired region, if necessary. A thickener may be added.

As a means for containing the aqueous reaction solution in the cellulose fibers in a desired region of the sheet, the aqueous reaction solution is applied by a printing method such as gravure, screen, flexo or the like, or an application means by a spray method is adopted. be able to. Further, the shape of the region containing the aqueous reaction solution, the size, and the ratio of the containing portion to the entire sheet can be arbitrarily determined depending on the containing method and the use situation, but the shape is a polka dot shape, a slit shape, or these. And the like are preferably used. The ratio of the area of the cellulose-based fiber containing the aqueous reaction liquid to the total area of the sheet is preferably 0.2 to 0.9 of the area of the liquid-containing area / the total area of the sheet.

The content of the aqueous reaction liquid in the liquid-containing region is such that the molar ratio of carboxyalkylating agent to glucose residue is 0.7 to 2.0 (mol / mol) in terms of carboxyalkylating agent / glucose residue. Appropriate. When the molar ratio is less than 0.7, it becomes impossible to obtain a substitution degree higher than 0.35, and therefore a sheet having a high water absorption cannot be obtained.
On the contrary, even if the molar ratio is 2.0 or more, the substitution degree hardly increases, which is economically disadvantageous. The sheet having a region containing the aqueous reaction solution is, if necessary for the purpose of suppressing the decomposition of the carboxyalkylating agent in the aqueous reaction solution and increasing the reaction efficiency, at a temperature of 50 to 150 ° C. for 10 to several seconds. By heating with blowing under the conditions, a part of the water of the contained aqueous reaction solution is evaporated and removed, and the proportion of water per content weight of the aqueous reaction solution is adjusted to 20 to 60% by weight. It The method of evaporating 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, the evaporation temperature is too long even in the above temperature range.
For example, after 30 minutes or more, carboxyalkylation progresses or ends during evaporation, and the effect of the present invention cannot be obtained. Carboxyalkylation hardly progresses under the above-mentioned evaporation conditions (substitution degree is 0.1 or less), and such evaporation is performed in a dryer or in a reaction vessel while applying hot air in the above temperature range. Is convenient. In that case, if the proportion of water in the aqueous reaction solution contained in the composite sheet after evaporation of water is 20% or less, the degree of substitution will decrease, and the resulting water-absorbent sheet or nonwoven fabric will remarkably It turns yellow and must be avoided. Further, when the proportion of water is higher than 60%, the effect of imparting water absorption may be reduced.

Immediately after adjusting the proportion of water in the aqueous reaction solution in this manner, as described above, almost no carboxyalkylation has yet occurred. Therefore, the composite sheet is heated thereafter to carry out carboxyalkylation and crosslinking. Let the reaction of. In this case, even if water evaporates during heating and escapes to the outside of the system, the proportion of water in the aqueous reaction solution is preferably maintained within the above range. In this operation, a sheet partially containing an aqueous reaction solution is continuously passed through a heating device, or a sheet is covered with a sheet to make a sealed state, and then the reaction temperature is batchwise heated to a range of 50 to 110 ° C. This can be done easily. When the reaction temperature is 50 ° C or lower, it takes a long time to complete the reaction, and conversely, the reaction temperature is 1
When the temperature is higher than 10 ° C., the degree of substitution and the amount of water absorption of the resulting water-absorbent nonwoven fabric tend to be low, and moreover, the water-absorbent sheet is often yellowed, which is not suitable.

The heating may be performed from the outside of the sheet containing the aqueous reaction solution, but when the amount of the sheet is large, the temperature range may naturally reach due to the reaction heat of carboxyalkylation. In such a case, the object may be achieved only by leaving it in a closed condition or under an open condition. The reaction time cannot be determined regardless of the reaction temperature, but 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.
Since the reaction is completed even if the reaction time is longer than the time, it is meaningless if the reaction time is further extended.

As described above, the pure water absorption of the cellulosic fiber having the water absorbency in the region having the cross-linking bond and the carboxyalkyl group provided in the sheet is mainly determined by the substitution degree of the carboxyalkyl group and the crosslink density. To be done. The pure water absorption is theoretically higher as the substitution degree of the carboxyalkyl group is higher, but practically, the substitution degree is 0.35 to 0.35.
0.8 is suitable. The upper limit of the degree of substitution is about 1.2,
Even if the water content is increased above 1.2, the water absorption amount will be almost saturated, and the water absorption amount beyond that is economically useless. Further, a high degree of substitution exceeding 0.8 cannot be achieved unless the reaction is repeated at least twice. Therefore, as in the present invention, the aqueous reaction solution is partially contained only in a predetermined region, The method of imparting water absorbability by allowing it to do so is difficult to carry out because it is difficult to secure a region that does not contain the aqueous reaction solution when the aqueous reaction solution is repeatedly added to the cellulosic fibers.

On the other hand, if the degree of substitution is less than 0.35, a sufficient amount of pure water absorption will not be imparted to the water-absorbing cellulosic fibers in the above region. The degree of substitution within the scope of the present invention described above is the amount of the carboxyalkylating agent and the alkali metal hydroxide added to the cellulosic fibers, the proportion of water in the aqueous reaction solution after evaporation of water, the reaction temperature, the reaction time, etc. It is determined by the total effect of the above. If necessary, these factors are appropriately selected, combined and adjusted to obtain a suitable degree of substitution. The pure water absorption increases as the crosslink density decreases, but if it is too small, the strength of the gel when absorbing water will be weak,
Further, since the water-soluble carboxyalkyl cellulose salt remains, it becomes unsticky and is not preferable. 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 fibers in the above-mentioned region of the sheet after the carboxyalkylation and the cross-linking reaction contain a large amount of inorganic salts and decomposed products of the carboxyalkylating agent, and therefore it is necessary to remove them for purification. Any known method may be used for this. For example, impurities are effective 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, and by repeating the washing, for example. Can be removed.

As described in detail above, the present invention is prepared by dissolving a carboxyalkylating agent, an alkali metal hydroxide and a crosslinking agent in water in a desired region of a sheet containing synthetic fibers and cellulosic fibers. An area having a carboxyalkyl group in which the cellulosic fiber is crosslinked by heating and carboxyalkylating after containing an aqueous reaction solution, and a cellulosic fiber having neither a carboxyalkyl group nor a crosslink bond. Is a water-absorbent sheet provided in any mixture.

Since the water-absorbent sheet of the present invention has the above-mentioned structure, when it is used in an absorbent body having a multilayer structure of two or more sheets, the liquid which comes into contact with the absorbent sheet is partially absorbed in the water-absorbent region of the sheet. The absorbed and non-absorbed liquid passes through the region where neither cross-linking nor carboxyalkyl group is present and reaches the next water-absorbing sheet, where again some liquid is absorbed in the water-absorbing region and non-absorbed liquid does the same. It is further transferred to the next absorbent sheet, that is, it has both transfer performance (having both liquid diffusion and temporary storage properties) and water absorption performance, thus preventing gel blocking and preventing liquid Since it is not absorbed and does not overflow laterally from the absorber, the liquid absorption efficiency is extremely high, and excellent shape stability can be maintained even after absorbing liquid. Suitable for a wide range of applications, including hygienic materials such as disposable diapers and sanitary products, soil water retention materials, agricultural materials such as nursery sheets, food freshness retention materials, food materials such as dehydration materials, and building materials such as dew condensation prevention sheets for buildings Used for.

[0029]

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

Example 1 A spunbonded non-woven fabric was prepared in which polypropylene filaments were accumulated and which had a large number of spot fusion zones in which the polypropylene filaments were self-fused together. The fineness of the long fibers constituting this nonwoven fabric was 2.5 denier, and the basis weight of the nonwoven fabric was 12 g / m ² . On the surface of this non-woven fabric,
Paper sheets obtained by wet papermaking were laminated using bleached softwood kraft pulp fibers (NBKP). This paper sheet had a basis weight of 76 g / m ² and a density of 0.52 g / cm ^{3 as} measured by the method described in JIS P 8124. The resulting laminate is then placed with the paper sheet on top,
The spunbonded non-woven fabric was placed on the transfer conveyor formed of a wire mesh so that it was located below. Then, while transporting this laminate at a speed of 20 m / min, the pore size was 0.1
Using a high-pressure water column flow jetting device in which 2 mm nozzle holes are arranged in a staggered pattern at 0.64 mm intervals, a high-pressure water column flow is jetted at a water pressure of 40 kg / cm ² , and the high-pressure water column flow from the surface of the paper sheet to the nonwoven fabric side. After applying, it was dried with a dryer at 120 ° C.

As described above, the pulp fibers constituting the paper sheet and the long fibers constituting the spunbonded non-woven fabric were entangled with each other to prepare a composite sheet in which both were integrated. The basis weight of this sheet was 80 g / m ² . This composite sheet was cut into a size of 20 cm × 30 cm to prepare a sheet having a weight of 4.8 g. Next, sodium hydroxide 8.38%, sodium monochloroacetate 24.40
%, Ethylene glycol diglycidyl ether 0.68
% And 66.54% water to form an aqueous reaction solution,
In order to examine the adhesion state of the reaction solution, a blue aqueous pigment (trade name: TB-710GA, manufactured by Dainichiseika Co., Ltd.) was added in an amount of 0.1% per weight of the reaction solution. Then, the aqueous reaction solution was applied to the paper sheet side of the composite sheet by using a gravure coater having a printed pattern with a wavy stripe pattern having a cycle of 14 mm, an amplitude of 1 mm and a line width of 3 mm and a sine curve of 6 mm pitch, and contained. . In this case, the area ratio of the area containing the aqueous reaction liquid was 50% with respect to the total area of the composite sheet on the paper sheet side. Further, the content of the aqueous reaction solution in the partial region contained in the composite sheet was 3 g of the aqueous reaction liquid (carboxymethylating agent / glucose residue = 1.3 Mol / mol).

After that, the electrothermal hot-air drier equipped with an exhaust facility is kept at 50 ° C., and while evacuation is performed, the composite sheet coated with the aqueous reaction solution and contained therein is put in this drier for 5 minutes to evaporate water. It was The proportion of water in the aqueous reaction solution contained in the sheet was 42%. This sheet was put in a polyethylene bag and put in a dryer kept at 50 ° C. for 3 hours to heat it to carry out carboxymethylation and crosslinking of NBKP. After the reaction is completed, the composite sheet is dipped in 70% aqueous methanol solution, sandwiched between filter papers and pressed.
This sheet was repeated, and the sheet was thoroughly washed. Finally, the washed composite sheet was dipped in 100% methanol, again sandwiched between filter papers and pressed, and then air-dried to obtain a water absorbent sheet.

Using this water absorbent sheet, the degree of substitution, the amount of pure water absorbed and the rate of absorption were measured by the following test methods. Test Method (1) Degree of Substitution 1 g of a carboxyalkyl (methyl) -modified portion colored with a pigment was collected from the test sample and collected. This sample was placed in a flask, 50 ml of methanol-hydrochloric acid solution (mixed aqueous solution in which 70% methanol aqueous solution was dissolved in hydrogen chloride to a concentration of 1 mol / liter) was added, and the mixture was left for 1 hour and then thoroughly washed with methanol. Then, the hydrochloric acid was completely removed, and it was air dried. Then, the air-dried sample was placed in a 300 ml Erlenmeyer flask, 20 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. Titration was performed as an indicator, and the substitution degree was calculated by the equations (1) and (2). Y = 0.1A-0.1B ... (1) Substitution degree = 162Y / (1000W-80Y) ... (2) However, A: The amount of 0.1N sodium hydroxide solution (m.
l) B: amount of 0.1 N hydrochloric acid (ml) Y: amount of carboxyalkyl (methyl) group (milliequivalent) W: weight of carboxyalkyl (methyl) cellulose (g)

(2) A test sample having a pure water absorption of 1 g was enclosed in a 250-mesh nylon mesh bag having a size of 10 cm × 10 cm, and deionized water was distilled through an ion exchange resin to obtain a pure sample. Immerse in water for 10 minutes to absorb water, then hang it up and hang it for 10 minutes to drain water, then measure the weight of the test sample, and measure the pure sample absorbed per 1 g of absolutely dried test sample. The amount of water absorption was indicated by the weight (g). (3) Absorption rate 10 cm x with a circular hole with a diameter of 2.5 cm in the center
After placing 4 stainless steel plates of 10 cm in size on the test sample, 50 ml of artificial urine of the following composition was injected through the hole in the central part so that the liquid would not overflow from the circular hole. The time required for absorption into was measured and used as the absorption rate. Composition of artificial urine Urea 1.9% NaCl 0.8% CaCl ₂ 0.1% MgSO ₄ 0.1% Distilled water 97.1%

Example 2 80 g / gram of basis weight obtained by hydroentangling the long fibers of the spunbonded nonwoven fabric used in Example 1 and the pulp fibers of the paper sheet.
the composite sheet of m ² was prepared in the take-up. An aqueous reaction solution prepared with the same formulation as in Example 1 was also prepared. Next, a spray type coating device, in which nozzles capable of intermittently discharging a fixed amount of droplets are arranged in a line at a pitch of 15 mm, is installed above the composite sheet, and the composite sheet is transferred at a speed of 5 m / min while water-based. The reaction solution was discharged from each nozzle of the spray-type coating apparatus at an interval of 0.18 seconds so that the amount of the solution was 0.05 ml / times, and was applied in the form of dots on the paper sheet side of the composite sheet to be contained. In this case, the area ratio of the area containing the aqueous reaction solution was 35% with respect to the total area of the composite sheet on the paper sheet side.

The content of the aqueous reaction liquid in the region containing the aqueous reaction liquid on the composite sheet is 3.9 g (carboxymethylating agent / glucose residue = 1 per 1 g of the absolutely dry composite sheet in the containing region). It was 0.7 mol / mol). A composite sheet containing this aqueous reaction solution is 20 cm × 30 c
After cutting to a size of m, the same operation as in Example 1 was repeated except that the content of water in the aqueous reaction liquid was adjusted to 26% by heating in a dryer for 4 minutes to evaporate the water and absorb the water. A sex sheet was obtained. Using this water absorbent sheet, a test was conducted in the same manner as in Example 1.

Comparative Example 1 An absorbent sheet was prepared by repeating the same operation as in Example 1 except that the composite sheet was impregnated in an aqueous reaction solution to carboxymethylate all pulp fibers contained in the sheet. did. A test was conducted in the same manner as in Example 1 using this water absorbing sheet. Comparative Example 2 The composite sheet having a basis weight of 80 g / m ² used in Example 1 was used as 20
It was cut into a size of cm × 30 cm and subjected to the same test as in Example 1 without carrying out carboxymethylation and crosslinking reaction. The results obtained in Examples 1-2 and Comparative Examples 1-2 are shown in Table 1.

[0038]

[Table 1]

As can be seen from Table 1, the absorbent sheet of the present invention is slightly inferior in the amount of water absorption per unit weight, but when a plurality of layers are used in a multi-layered structure to absorb water, even if gel blocking occurs, gel Since it has a portion where blocking does not occur at all, the absorption of the liquid is not hindered and is rapidly diffused and absorbed into the absorber having the multilayer structure, so that the liquid absorption efficiency is extremely high (Examples 1 to 1). 2). On the other hand, when a water absorbent sheet obtained by carboxyalkylating all the pulp fibers contained in the composite sheet is used as an absorbent body having a multilayer structure, the first side water absorbent sheet on the liquid side to be absorbed is However, since gel blocking occurs and the diffusion of the liquid is hindered, it is difficult for the liquid to diffuse into the water-absorbent nonwoven fabric layer of the second and subsequent layers, and it takes a considerably long time for absorption (Comparative Example 1). When neither carboxyalkylation nor cross-linking reaction was performed, the water absorption rate was remarkably high, but the pure water absorption rate was low, and liquid leakage occurred when measuring the water absorption rate (Comparative Example 2), both of which are not suitable for practical use. It was

[0040]

As described above, according to the present invention, a cellulosic fiber is provided with a high water-absorbing region having a carboxyalkyl group and a crosslinking bond and a low water-absorbing region having neither a carboxyalkyl group nor a crosslinking bond. In addition, it has the effect of providing a water-absorbent sheet having both excellent transfer performance and water-absorption performance, and particularly when the absorbent body has a multi-layer structure, the absorption speed is remarkably excellent.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location D04H 1/42 A61F 13/18 307G D21H 19/10 D21H 1/34 A // D06M 13/188 D06M 13/20

Claims (1)

[Claims] 1. A water absorbent sheet comprising synthetic fibers and cellulosic fibers, wherein the cellulosic fibers in a desired region of the sheet have a crosslinked carboxyalkyl group with a substitution degree of 0.35 to 0.8, Water absorption characterized in that the cellulosic fiber of the portion other than the region of the sheet does not have a carboxyalkyl group and a cross-linking bond, and a high water-absorption region and a low water-absorption region are provided mixedly in the sheet. Sex sheet.